Semiconductor devices are built up using a number of silicon compound and metal material layers. Some layers can be grown from another layer; for example, an insulating layer of silicon oxide can be grown over a layer of silicon by oxidizing the silicon surface. Other layers are deposited using various techniques, such as vacuum evaporation, sputtering, and chemical vapor deposition (CVD). The layers are patterned with photoresists to remove selected portions. The remaining material forms circuit features that will eventually make up an integrated circuit.
Metal etch processes commonly employ halogen etch gases, such as chlorine and bromine gas. Silicon etch processes also employ halogen etch gases, such as nitrogen trifluoride, sulfur hexafluoride, and tetrafluoromethane. Halogen and halogen-bearing etch gases react with aluminum surfaces of process equipment to form halogen etch contaminants, such as aluminum fluoride and aluminum chloride.
Halogen etch contaminants and other process byproducts collect on interior surfaces of process equipment. Thus, after substantial use, contaminant films accumulate on components and surfaces within the reaction chamber. As these films grow inside the chamber, they become increasingly troublesome sources of contaminants. The reaction chamber, including internal components, must therefore be periodically cleaned or replaced.
Halogen etch contaminants are difficult to remove. This difficulty is exacerbated when the contaminated surfaces are difficult to access. Aluminum electrodes that double as gas-distribution plates (commonly known as “showerheads”) are particularly difficult to clean. Showerheads typically include tens to hundreds of very small holes that become clogged with aluminum fluoride or aluminum chloride during etch processes that employ fluorine or chlorine gas species. Showerheads manufactured by Applied Materials and Tokyo Electron Limited are typical.
There are two common types of showerheads. In the first type, the entire electrode surface, including within the holes, is anodized aluminum. In the second type, each hole includes a VESPEL insert. VESPEL is a type of plastic that inhibits formation of contaminants to minimize the need for cleaning.
Showerheads with anodized aluminum holes are conventionally cleaned by bead blasting. In this laborious process, the perforated surface of a showerhead is “masked” prior to bead blasting with a plate that has precision-drilled holes matching the holes in the showerhead. Unfortunately, bead blasting removes some of the anodized material from the showerhead, reducing the useful life of expensive components. Moreover, bead blasting produces excessive particulate contamination from the component surface and blast media.
Showerheads with inserts are conventionally cleaned by CO2 blasting. This method is similar to bead blasting, but the beads are substituted with CO2 ice particles that collide with and remove aluminum fluoride, aluminum chloride, and other contaminants. The effectiveness of this method reduces with holes size, making it difficult or impossible to properly clean showerheads. Carbon dioxide is also used on anodized aluminum holes to remove loose contaminants, but is ineffective at removing aluminum chloride or aluminum fluoride chemically bound to aluminum surfaces.